The present invention is generally directed to apparatus and methods for ultrasound imaging. More particularly, the present invention is directed to apparatus and methods for achieving a compound mode.
In conventional ultrasound imaging systems, there is an array of ultrasonic transducers. The ultrasonic transducers are used to transmit an ultrasound beam and then receive the echoes from an object being studied. An array for ultrasound imaging typically has a plurality of transducers positioned in a line and driven with separate voltages. By selecting the time delay or phase and amplitude of the applied voltages, the individual transducers can be controlled to produce ultrasonic waves. The ultrasonic waves combine to form a net ultrasonic wave that travels along a preferred vector direction and is focused at a selected point along the beam.
Multiple firings may be used to obtain data that represents the same anatomical information. The beamforming parameters of each of the firings may be varied to provide a change in maximum focus or otherwise change the content of the received data for each firing. For example, the multiple firings may comprise successive beams transmitted along the same scan line with the focal point of each beam being shifted relative to the focal point of the previous beam. By changing the time delay and amplitude of the applied voltages, the beam with its focal point can be moved in a plane to scan the object.
Reception of reflected sound by a transducer involves the same principles as transmitting sound. The voltages produced at the receiving transducers are summed so that the net signal is representative of ultrasound echoes reflected from a single focal point in the object. As with the transmission mode, this focused reception of the ultrasonic energy is achieved by separate time delays (and/or phase shifts) and gains provided to the signal by each receiving transducer.
Imaging with conventional ultrasound systems can result in images containing a significant amount of speckle. Speckle is an imaging artifact produced from interference patterns of multiple receive echoes. Speckle appears as mottling which is manifest as black holes in the image.
A method has been proposed to reduce speckle by combining vector data from multiple ultrasound firings for different portions of a scan line. The input vector data from multiple firings is combined to take advantage of the best range(s) of data from each receive firing. One or more lines are fired at the same location, with the lines having different focus points or depths. Compounding of echoes from the multiple firings (focused to different depths) is performed over only a fraction of the length of the scan line. Compounding portions of scan lines from echoes of different transmissions does not entirely remove speckle. A need exists for more effective methods and apparatus for reducing the amount of speckle in ultrasound images.
A conventional compounding technique is the compounding of frames rather than lines. The technique of compounding of frames has a disadvantage of movement artifact.
Conventional multifocus algorithms create zones where the near field and far field come together and may create image impressions if an operator were to move from the near field to the far field in a small range. Thus, there is a need for an ultrasound mode that reduces the border between the near field and the far field.
Some conventional ultrasound techniques do not have much penetration. Examination of some patients, particularly patients having high adipose content tissue, may require ultrasound capable of deeper penetration. Accordingly, there is a need for ultrasound devices or techniques that provide greater penetration.